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Revenue from Contracts with Customers Narrative (Details) | 12 Months Ended
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Sep. 30, 2019
Transferred over Time [Member] |
Disaggregation of Revenue [Line Items] |
Percent of Revenue by Recognition Timing | 2.00%
Transferred at Point in Time [Member] |
Disaggregation of Revenue [Line Items] |
Percent of Revenue by Recognition Timing | 98.00%

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- Definition Percent of Revenue by Recognition Timing + References No definition available. + Details
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Namespace Prefix: | mwa_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |